Just bite on the bacteria

Few medical breakthroughs arouse such excitement as one that promises to end trips to the dentist. Cavities don't kill, but we've all been to the dentist and most of us hate it.

Professor Jeffrey Hillman's new treatment won't put dentists out of a job, but it could leave them with a lot less to do. And the people who have most to lose are worried. "Some dentists don't believe it will be successful. They see it as a threat," says Hillman.

The university of Florida researcher has come up with a brilliantly simple way to tackle tooth decay. Using the genetic engineering techniques best known for creating GM food he has engineered a harmless version of the bacteria that rots our teeth.

The villain of the piece is Streptococcus mutans, a naturally occurring bacteria that lives in our mouths. Streptococcus mutans is busy on your teeth right now, happily feeding itself on whatever sugar it can find. It provides us with some benefits - producing important vitamins and giving protection against nastier bacteria - but our teeth pay the price. In return for keeping it alive, the bacteria produces lactic acid which attacks tooth enamel and causes cavities.

Hillman manipulated Streptococcus DNA to remove the gene responsible for producing lactic acid. The new bacteria - known as an effector strain - thrives on sugar but, unlike the original bacteria, does not produce lactic acid. If this strain were used to replaced the original strain on our teeth the majority of cavities could be prevented.

The new strain was tested first on rats who, like humans, suffer the effects of the Streptococcus mutans. No only did the effector strain colonise the rat's teeth, it actually dominated the original strain. Ironically, feeding the rats with a high-sugar diet helped the new strain replace the old one and hence reduced the amount of lactic acid. The long-term prospects are also good - the new strain appears to be stable and to stay permanently on teeth.

Clinical trials start this year and Hillman is confident that they will confirm the safety and effectiveness of the new strain. But convincing the authorities to license his treatment may not be his biggest challenge. After a slow start, opposition to GM technologies is taking off in the US. The idea of gargling with a genetically modified bacteria is unlikely to appeal, regardless of what clinical trials prove.

Hillman is confident the public will see the benefits. "This approach is really a lot more natural than most of the antibacterial approaches in use today. Over the next 100,000 or so years, natural selection would act on Streptococcus mutans to reduce its virulence and on humans to increase their resistance to Streptococcus mutans. This therapy is an attempt to speed up this process by doing in the lab in 20 years what it would take nature 100,000 years."

If Hillman's idea does pass the clinical trials and a sceptical public can be persuaded, the treatment could be in use in two to three years. "The ideal application would be to treat infants when their first teeth appear. They normally acquire Streptococcus mutans via contaminated saliva from their mother," says Hillman. "The child would simply visit their dentist for a squirt of solution on their teeth."

Since the new strain dominates over the old this initial treatment should last for a lifetime. And the work with rats suggests that adults - who already have Streptococcus mutans on their teeth - will be protected by the same simple process.

Streptococcus isn't the only bacteria that causes decay, but it is reckoned to be responsible for the majority of cavities. And even if it doesn't eliminate tooth decay, it might leave dentists with a little more time on their hands.